Recent studies challenge long-held paradigms about the role of specific insulin target tissues in whole body insulin action and in the pathogenesis of insulin resistance. Studies in this application will investigate the importance of the Glut4 glucose transporter in muscle and adipose tissue, and the dynamic interactions by which altering glucose transport in one of these tissues may cause insulin resistance in other insulin target tissues including liver. The overall goal is to determine the role of glucose transport in adipose tissue and in muscle in whole body glucose homeostasis. Our preliminary data indicate that markedly reducing Glut4 expression selectively in adipose tissue causes insulin resistance and glucose intolerance which are as severe as knocking out Glut4 from muscle. This is important since in humans with obesity and type 2 diabetes, Glut4 expression is down-regulated in adipocytes but not in skeletal muscle. We also find that mice with muscle specific Glut4 knockout eventually become insulin resistant in fat and liver. We will investigate the molecular mechanisms for these effects. Specific aims are: 1) To determine the mechanisms by which altering Glut4 expression selectively in adipocytes affects whole body glucose homeostasis. 2) To determine what genes/molecules mediate the effects of altered Glut4 expression in adipocytes on whole body glucose homeostasis. 3) To determine the role of brown adipose tissue in the insulin resistance caused by reduced Glut4 expression is adipose tissue. 4) To determine the mechanisms by which altering Glut4 expression selectively in muscle affects insulin action in other tissues. 5) To determine whether combined knockout of Glut4 from adipose tissue and muscle will lead to greater insulin resistance than knockout from either tissue alone and how this is affected by genetic background. These studies will lead to a better understanding of the mechanisms for regulation of glucose homeostasis and the role of impaired glucose transport, which is present in adipocytes and muscle of humans with obesity and type 2 diabetes, in the pathogenesis of insulin resistance. Our goal is to find new therapeutic targets to prevent or ameliorate type 2 diabetes.